The antennas of certain airport radars carry out an electronic scan of the beam in a single plane. In the plane in which the beam is fixed, so as to reduce costs, sub-arrays of N radiating elements are fed by a single active channel, by means of an RF divider 1:N, a divider being made up of an assembly of power splitters, linked together by sections of transmission line.
In order to implement the front-end RF divider between the active channel and the N radiating elements, the use of stripline dielectric technology is known, compatible with the multi-layer printed circuit which also contains the active components and the radiating elements.
The dielectric used is typically a commercially available substrate which has the advantage of great technological maturity and a low cost. Nevertheless it has the drawbacks of a low thermal conductivity of 0.64 W/(m·K) and high dielectric losses, of the order of 10 dB/m or even more, which impair the emitting (EIRP) and receiving (G/T) performances of the antenna.
At the end of the 1990s, a method was developed for heat dissipation in an air-line structure in a metallic waveguide. This cooling method, consisting in inserting, at regular intervals along the line, ceramic pads between the central path of the air line and the metallic ground of the waveguide, was used in an RF divider made up of hybrid rings for the demonstration antenna SAREX (“Experimental X-Band SAR Radar”). This structure has the drawback of relatively high volume and mass; it cannot be integrated in a multi-layer printed circuit.
Consequently, to this day there remains a need for a printed circuit simultaneously satisfying all of the aforementioned demands, in terms of minimizing its dielectric losses and its heating.